Method and installation for irradiating bulk material

ABSTRACT

The present invention is related to method for irradiating bulk material, particularly for treatment of food products such as grain, characterised in that in the case of a failure of said irradiation, the untreated bulk material is separated from the treated material and subsequently transported back towards the beginning of the process, in order to be treated. The invention allows to avoid re-treatment of large quantities of material, and provides a clear separation between contaminated and uncontaminated parts of the installation.

FIELD OF THE INVENTION

[0001] The present invention is related to a device for the irradiationof bulk products, in particular food products in bulk, such as grain.

STATE OF THE ART

[0002] The disinfestation of grain by irradiation is a known technique.A radiation source, such as a beam of accelerated electrons or a beam ofX-rays is preferably used for this purpose. Many known techniques andinstallations, such as the one described in EP-A-705531 are related toirradiation of particles, preferably grain, as it falls through avertical shaft. When the irradiation is stopped during the process, forexample due to a machine failure, it is impossible to separate thetreated from the untreated grain. Even if the supply is stopped veryquickly, a minimum amount of untreated material will fall through theshaft without being irradiated, and join the already treated material,mixing with it. This causes large amounts of grain to be re-treated inorder to be sure that no untreated grain mixes with the already treatedbatch. Also, it requires parts of the installation which are normallyonly in contact with treated material, to be thoroughly cleaned anddisinfected after any machine failure. An additional drawback of thefree fall system is that the bulk material may be damaged in the fall.

AIMS OF THE INVENTION

[0003] The present invention aims to provide a method and installationfor irradiating bulk material, such as grain, in such a way that ,incase of failure of the radiation source, one can separate untreated fromtreated material.

SUMMARY OF THE INVENTION

[0004] The present invention is related to a method for irradiating bulkmaterial, particularly for treatment of food products such as grain,comprising the steps of

[0005] providing a continuous supply of said bulk material onto aconveying device, which transports said material in an essentiallyhorizontal direction, said conveying device being at least partiallyplaced inside an irradiation cell, said conveying device being exposedto an irradiation beam, allowing treatment of said material,

[0006] evacuating the treated material at the end of said conveyingdevice, characterised in that, in the case of the loss or insufficiencyof the irradiation, the untreated and badly bulk material that shouldhave been treated properly, is separated from the fully treated bulkmaterial.

[0007] According to a preferred embodiment, said method furthercomprises an additional recuperation step taking place in the case ofinsufficiency or loss of the irradiation, said additional stepconsisting of transporting said untreated bulk material, after beingseparated from the treated bulk material, towards the beginning of saidconveying device, in order for said untreated bulk material to betreated.

[0008] Said separation and recuperation are preferably obtained byperforming the following steps

[0009] slowing down said conveying device at a predefined decelerationrate,

[0010] blocking, inside said irradiation cell, the normal exit path ofirradiated material out of said irradiation cell,

[0011] creating, inside said irradiation cell, a new exit path, out ofsaid irradiation cell,

[0012] re-activating said conveying device, thereby forcing the materialthat was present on said device to be evacuated from the irradiationcell through said new exit path,

[0013] transporting said material that was present on said conveyingdevice back to the beginning of said conveying device.

[0014] Said step of creating a new exit path is preferably performed byrotating a hinged plate around an axis, over a predefined angle. Saidstep of providing a continuous supply preferably comprises the followingsubsteps:

[0015] providing a continuous supply of said material to an inputhopper,

[0016] at a signal corresponding to an ‘empty’ condition in a weighingstation, transferring said material to said weighing station, by openinga shutter underneath said input hopper,

[0017] at a signal corresponding to the ‘full’ condition of saidweighing station, closing said shutter underneath said input hopper,weighing said material, and transferring said material to a bufferhopper, by opening a shutter underneath said weighing station,

[0018] transferring a continuous supply of said material from saidbuffer hopper, onto said conveying device.

[0019] Said conveying device may be a conveyor belt and wherein a layerof a constant width and thickness is preferably provided onto saidconveyor belt. Said layer of a constant width is preferably created bysupplying said material onto said belt by a slide, said slide beingequipped with guides, said guides having preferably the shape of aninverse V. A layer of a constant thickness is preferably created by wayof a horizontal scraper.

[0020] The invention is equally related to an installation forirradiating bulk material, in particular for treatment of food productssuch as grain, comprising the following elements:

[0021] a device for creating a beam suitable for irradiation purposes,

[0022] an irradiation cell,

[0023] a supply system for providing a continuous supply of material tosaid irradiation cell,

[0024] a first transport device for evacuating said material afterirradiation from said irradiation cell,

[0025] means for changing the exit path of said material afterirradiation from a first exit path, leading to said first transportdevice to a second exit path.

[0026] The installation of the invention preferably further comprises asecond transport device for transporting back towards said supplysystem, from said second exit path, at least the untreated materialpresent in said irradiation cell, after a failure of said irradiation.

[0027] Said means for changing said exit path preferably comprises ahinged plate, operated by a cable, connected to a winch.

[0028] According to the preferred embodiment:

[0029] said supply means consist of a first hopper, above a weighingstation, comprising a second hopper and placed in turn above a bufferhopper, leading to a screw conveyor, which takes the material throughthe wall of the irradiation cell,

[0030] a conveyor belt is placed wholly inside said irradiation cell,said conveyor belt comprising vertical ridges perpendicular to thetranslation of said conveyor belt,

[0031] a slide is placed between said screw conveyor) and said conveyorbelt, said slide being equipped with guides, said guides having theshape of an inverse V,

[0032] said first and second transport devices are both screw conveyors,said installation further comprising two material elevators fortransporting the material after said first and second screw conveyors,said second material elevator transporting the material back to saidbuffer hopper in case of an irradiation failure.

[0033] According to a second embodiment

[0034] said supply means consist of a first hopper, above a weighingstation, comprising a second hopper and placed in turn above a bufferhopper, leading to a screw conveyor, which takes the material throughthe wall of the irradiation cell,

[0035] said screw conveyor transports said material underneath said beamfor irradiation,

[0036] said first and second transport devices are both screw conveyors,said installation further comprising two material elevators fortransporting the material after said first and second screw conveyors,said second material elevator transporting the material back to saidbuffer hopper in case of an irradiation failure.

SHORT DESCRIPTION OF THE DRAWINGS

[0037]FIG. 1 represents a schematic view of an installation and of theprocess flow according to the present invention.

[0038]FIG. 2 represents a detailed view of an installation according toa preferred embodiment of the present invention.

[0039]FIG. 3 represents a detail of the conveyor belt used duringirradiation, according to a preferred embodiment of the presentinvention.

[0040]FIG. 4 represents a detail of the slide used in the installationaccording to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041]FIG. 1 shows a schematic view of the essentials in the processflow according to the method of the invention. The flow has to beclearly divided into two parts: untreated 100 and treated material 101.The transition from untreated to treated material is made in theirradiation cell 3.

[0042] According to a preferred embodiment, this material consists ofgrain, to be irradiated for disinfestation purposes. It may howeverequally consist of other food products such as fruit or potatoes, or ofpolymer powder or pellets. The treatment of the latter may comprise agrafting or curing operation.

[0043] According to the preferred embodiment of the method of theinvention, the untreated material is brought by conveyors from thematerial storage (not shown) into a buffer hopper 1. A bulk materialtransport device 2, which is preferably a screw conveyor, feeds acontinuous stream of bulk material through the wall of the irradiationcell 3 and onto a slide 4, allowing the bulk material to slide onto aconveying device 5, which is preferably a horizontal conveyor belt. Thebelt is preferably made of stainless steel jointed slats, or stainlesssteel webbing. The conveying device may also be an “en-masse” conveyor,wherein the bulk material is transported in a u-shaped trough byhorizontal slats driven by chains. Special guides are present on theslide 4, in order to distribute the bulk material in a layer whichcovers the whole width of the conveyor belt 5. A blade system on theslide 4 will make sure that the bulk material layer thickness is equalto a predefined value over the whole width of the conveyor belt 5. Thesefeatures are explained in more detail further in this description. Oncethe bulk material is on the conveyor belt 5, it will be transportedunder the beam 6 and irradiated by this beam, which may be produced byan electron accelerator (not shown).

[0044] According to a second embodiment of the invention, the screwconveyor 2, slide 4 and conveyor belt 5 are replaced by one screwconveyor, and the bulk material is irradiated while being transported bythat one screw conveyor, underneath the beam. The preferred embodimenthowever comprises a screw conveyor 2, slide 4 and a horizontal conveyorbelt 5, carrying a layer of bulk material of a constant thicknessunderneath the beam 6.

[0045] The irradiation of the bulk material marks the transition fromthe untreated part 100 of the process to the treated part 101. Aftertreatment, the bulk material drops into a funnel, and is normally ledinto a transport device 7, preferably a second screw conveyor, whichtransports the bulk material out of the irradiation cell, through thewall of the cell, and feeds it into a bulk material elevator 8. Fromhere the bulk material is transported to the treated bulk materialstorage.

[0046] If a failure occurs during the irradiation process, the conveyorbelt 5 and the supply screw conveyor 2 are immediately stopped. Such afailure may be a complete loss of irradiation, or an insufficientirradiation due to a defect in the radiation source. Once the belt 5 isstopped, the material that is still on it is either badly orinsufficiently treated or not treated at all. Means 40 are provided tolead the untreated and badly treated bulk material that should have beentreated properly, not into the evacuation screw conveyor 7, but into atransport device 11, preferably a third screw conveyor, whichrecuperates the untreated and badly treated bulk material and sends itback to the start of the process flow, in order to be re-treated. Theuntreated and badly treated bulk material is evacuated through the screwconveyor 11 and fed into a bulk material elevator 12. On top of the bulkmaterial elevator 12 the bulk material is released into the bufferhopper 1 in order to be (re)treated.

[0047] The invention is characterised by the presence of the means 40for separating untreated and badly treated bulk material in case of anirradiation failure. This feature avoids any mixing of untreated andtreated materials. Also, a clear separation between untreated andtreated parts of the installation is present, allowing a quick restartin case of failure, obviating the necessity for a thorough cleaning ordisinfecting operation. In a preferred embodiment, the invention alsocomprises means for recuperating and recirculating (11,12) untreated andbadly treated bulk material. In the following, a preferred embodiment ofthe method and installation, including the means 40 for separating thematerials is described in detail.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0048]FIG. 2 shows a detailed view of an installation according to apreferred embodiment of the invention. FIG. 2b and 2 c show a frontaland side view of the whole of the installation, FIG. 2a shows a sideview of the supply system only. Many of the elements described above canbe recognised: irradiation cell 3, buffer hopper 1, supply screwconveyor 2, slide 4, conveyor belt 5, evacuation screw conveyor 7,recuperation screw conveyor 11, evacuation elevator 8, recuperationelevator 12. The beam is produced by an electron accelerator 20.

[0049] In order to provide a continuous supply of bulk material into theirradiation cell, an input hopper 21 and a semi-continuous weighingstation 22, comprising a weighing hopper 23 are present. The function ofthe input hopper 21 before the semi-continuous weighing station 22 is toallow a continuous bulk material flow coming from the untreated bulkmaterial storage and to stop the bulk material flow when thesemi-continuous weighing station 2-9 is weighing. Once the weighingstation is full, a shutter 24 is closing the supply from the inputhopper 21 into the weighing station 22. Once the bulk material has beenweighed, the shutter 25 of the weighing station opens and allows theweighing station's hopper 23 to be rapidly emptied into the bufferhopper 1. When the weighing station is empty, its shutter 25 is closedand the shutter 24 of the input hopper is opened again.

[0050] Being placed after the weighing station 22, the buffer hopper 1absorbs the discontinuities in the bulk material flow due to saidweighing station 22. The irradiation process requires a continuous bulkmaterial supply in order to obtain acceptable dose homogeneity andsufficient continuity of the process. The buffer hopper 1 also serves toaccept additional bulk material volumes coming from the recycling ofbadly treated or untreated bulk material (via the bulk material elevator12). The process control system will ensure that the buffer hopper 1does not get refilled with the bulk material to be recycled or with bulkmaterial coming from the weighing station 22 unless its level is lowenough to allow this.

[0051] From the buffer hopper 1, the bulk material is allowed through ashutter 26 into the screw feeder conveyor 2. This type of screw conveyoris preferably designed to be flood loaded and to regulate the volume ofmaterial being delivered at its output.

[0052] The bulk material, which is delivered in a controlled way by thescrew feeder 2, drops into a funnel 30 at the top of the slide 4. FIG. 3shows an enlarged image of the installation inside the irradiation cell.The slide 4 is constructed in such a way as to fulfil the followingrequirements:

[0053] At the outlet of the slide (bottom part) the bulk material flowis homogenous over the entire width of the conveyor belt 5: this isobtained by placing guides on the path of the sliding bulk material.These guides may be a set of chevrons 34 (inverse V) spread over thesurface of the slide as shown on FIG. 4.

[0054] The layer thickness on the conveyor belt is constant: this isobtained by placing an adjustable blade horizontally at the outlet endof the slide and at a fixed distance above the conveyor belt surface

[0055] According to the preferred embodiment, the width of the belt 5 is2 meters, and the thickness of the layer is controlled at 2.4 cm. With abelt speed of 44 meters per minute, this allows a bulk materialthroughput of 100 tonne per hour, considering the bulk material densityto be in the range between 0.75 and 0.8 tonne/m³. Using an electronaccelerator such as a Rhodotron or a Dynamitron, having a beam energy of5 Mev, and a power of 200 kW, would allow treatment of such a quantity.The thickness of 2,4 cm for a material having a density between 0,75 and0,8 tonne/m3 is chosen such that is penetrated by a 5 MeV electron beamin such a manner that the dose deposited in the upper layers of materialis approximately equal to the dose deposited in the lower layers.Assuming that 55% of the power is actually deposited in the grain, a 200kW beam can achieve a 4 kGy dose in a 100 tonne/hour throughput. A doseof 4 kGy is known to be enough to kill TCK (Tilletia Controversia Kuhn)in grain.

[0056] The bulk material is now homogeneously spread over the entirewidth of the conveyor belt 5 in a continuous layer. Vertical ridges 31on the conveyor belt, assure that the bulk material is not sliding onthe belt's surface when it first falls on the belt and needs to beaccelerated. The cross section of these vertical ridges 31 may be arectangle mounted perpendicularly to the conveyor's surface and to theconveyor's translation. However, such vertical ridges would impose apeak loading on the conveyor system each time such a ridge passes underan adjustable blade. In order to prevent such peak loading, the verticalridges are preferably given an inverse V-shape or a curved shape.

[0057] The bulk material is now transported through the acceleratedelectron beam. When no problems occur during the irradiation process thebulk material drops off the conveyor at the end and into a funnel 32.This is the funnel that feeds treated bulk material into the treatedbulk material screw conveyor 7.

[0058] If a problem occurs during the irradiation process, the conveyor5 is brought to a complete stop by gradually decelerating. Also, thescrew feeder 2 is stopped immediately. The conveyor belt's 5 length hasbeen calculated in order to be able to stop the belt completely beforeany of the untreated bulk material falls off at its end. Thedeceleration is to be calculated in order to assure that none of thebulk material of the conveyor is slung over the top of the verticalridges 31 during the deceleration. This assures that no untreated andbadly treated bulk material falls off the conveyor belt 5 and into thetreated bulk material funnel 32. The belt being stopped, it is nowneeded to recycle the untreated and badly treated bulk material which isstill on the belt 5 and on the slide 4, to the input of the supplysystem. According to the preferred embodiment shown in FIG. 3, a hingedplate serving as a shoot 40 is put into place, by traction on itscommand cable. The command cable is pulled on by an electric winch,which is placed in one of the product pits, outside the irradiationcell. This shoot 40 allows to empty the conveyor into the second funnel33 the untreated bulk material funnel. The conveyor belt is restarted ata low speed (e.g. 2 m/min) and with the shoot 40 in place, the bulkmaterial now falls into the untreated bulk material funnel 33, where itis fed into the untreated bulk material screw conveyor 11. The conveyor11 runs until the belt 5 as well as the slide 4 at the input side areempty, and the bulk material that was present on it is evacuated by theelevator 12, which leads it back to the buffer hopper 1. Once this isdone, the shoot 40 is put back to its normal position, to allow the bulkmaterial to fall once again into the treated bulk material funnel 32,and normal production can be restarted.

[0059] Both screw conveyors 7,11 for extracting the treated and theuntreated and badly treated bulk material out of the irradiation cell 3are regular screw conveyors. The throughput of the untreated bulkmaterial screw conveyor 11 can be much lower than the one for thetreated bulk material 7, since in normal operation all the bulk materialis treated. According to the preferred embodiment, the screw conveyor 7for the treated bulk material will have a throughput of 100 tonne perhour. The output side of both screw conveyors 7 and 11 is at the outsideof the irradiation cell in so-called product pits (51 and 50respectively).

[0060] The exact configuration of the bulk material elevators for thetreated bulk material 8 and the untreated bulk material 12 will stronglydepend upon the configuration of the site. The bulk material elevator 8for the treated bulk material will need to feed into a conveying systemthat transports the bulk material to the treated bulk material storage.The untreated bulk material screw conveyor 11 may either feed into abulk material elevator 12 for automatic recycling of the untreated bulkmaterial or into a bin. This bin, when full, will then need to bemanually emptied into the buffer hopper 1. To do so a lifting devicewill be needed, e.g. a crane.

[0061] In order to avoid throughput variations due to an irregular bulkmaterial feed flow, it is necessary to control the product supply system(21,22,1,2) through a control system. The control system will take careof flow management, e.g.: do not empty the weighing station 22 into thebuffer hopper 1 if it is filled with bulk material above a determinedlevel. The control system will also take care of the management ofaccelerator failure, by stopping the belt 5 and supply screw conveyor 2.

[0062] In order to perform the control tasks, a number of sensors areneeded. These are primarily level measurement sensors in the hoppers butthe control system also analyses equipment status information (conveyorspeed, conveyor running signal, . . .) and radiation source information(beam intensity, beam OK signal, . . .).

[0063] In order to avoid damage by irradiation, no sensitive partsshould be placed in the irradiation cell 3, in particular sensors whichcontain semiconductors or parts which are manufactured in radiationsensitive material. According to the preferred embodiment, all thisequipment is therefore placed outside the irradiation room.

[0064] The safety of the entire facility is controlled by a dedicatedsecurity control system. The security system controls access to theirradiation cell in respect to the status of the accelerator and thehandling equipment. Particular attention is given to the access to theproduct pits (50,51).

[0065] When the accelerated electrons collide with the air particles,ozone is generated. Another task of the safety system is the controlover the ozone extraction system, and the management of access to theirradiation cell in respect with ozone concentration.

1. A method for irradiating bulk material, particularly for treatment of food products such as grain, comprising the steps of: providing a continuous supply of said bulk material onto a conveying device (5), said conveying device being at least partially placed inside an irradiation cell (3), said conveying device (5) being exposed to an irradiation beam (6), allowing treatment of said material, evacuating the treated material at the end of said conveying device (5), characterised in that: said conveying device transports said material in an essentially horizontal direction, and in the case of the loss or insufficiency of the irradiation, the untreated and badly treated bulk material that should have been treated properly, is separated from the fully treated bulk material.
 2. The method according to claim 1, further comprising an additional recuperation step taking place in the case of insufficiency or loss of the irradiation, said additional step consisting of transporting said untreated bulk material, after being separated from the treated bulk material, towards the beginning of said conveying device (5), in order for said untreated bulk material to be treated.
 3. The method according to claim 2, wherein said separation and recuperation are obtained by performing the following steps: slowing down said conveying device (5) at a predefined deceleration rate, blocking, inside said irradiation cell (3), the normal exit path (32) of irradiated material out of said irradiation cell, creating, inside said irradiation cell (3), a new exit path (33), out of said irradiation cell, re-activating said conveying device (5), thereby forcing the material that was present on said device (5) to be evacuated from the irradiation cell through said new exit path (33), transporting said material that was present on said conveying device (5) back to the beginning of said conveying device (5).
 4. The method according to claim 3, wherein said step of creating a new exit path (33) is performed by rotating a hinged plate (40) around an axis, over a predefined angle.
 5. The method according to claim 1, wherein said step of providing a continuous supply comprises the following substeps: providing a continuous supply of said material to an input hopper (21), at a signal corresponding to an ‘empty’ condition in a weighing station (22), transferring said material to said weighing station (22), by opening a shutter (24) underneath said input hopper (21), at a signal corresponding to the ‘full’ condition of said weighing station (22), closing said shutter (24) underneath said input hopper (21), weighing said material, and transferring said material to a buffer hopper (1), by opening a shutter (25) underneath said weighing station (22), transferring a continuous supply of said material from said buffer hopper (1), onto said conveying device (5).
 6. The method according to claim 1, wherein said conveying device (5) is a conveyor belt (5) and wherein a layer of a constant width and thickness is provided onto said conveyor belt.
 7. The method according to claim 6, wherein said layer of a constant width is created by supplying said material onto said belt (5) by a slide (4), said slide being equipped with guides, said guides having preferably the shape of an inverse V.
 8. The method according to claim 6, wherein a layer of a constant thickness is created by way of a horizontal scraper.
 9. An installation for irradiating bulk material, in particular for treatment of food products such as grain, comprising the following elements: a device (20) for creating a beam (6) suitable for irradiation purposes, an irradiation cell (3), a supply system (21,22,1,2) for providing a continuous supply of material to said irradiation cell (3), a first transport device (7) for evacuating said material after irradiation from said irradiation cell (3), characterized in that said installation further comprises a means (40) for changing the exit path of said material after irradiation from a first exit path (32), leading to said first transport device (7) to a second exit path (33).
 10. The installation according to claim 9, further comprising a second transport device (11) for transporting back towards said supply system, from said second exit path (33), at least the untreated material present in said irradiation cell (3), after a failure of said irradiation.
 11. The installation according to claim 9, wherein said means for changing said exit path comprise a hinged plate (40), operated by a cable, connected to a winch.
 12. The installation according to claim 9, wherein: said supply means consist of a first hopper (21), above a weighing station (22), comprising a second hopper (23) and placed in turn above a buffer hopper (1), leading to a screw conveyor (2), which takes the material through the wall of the irradiation cell (3), a conveyor belt (5) is placed wholly inside said irradiation cell (3), said conveyor belt comprising vertical ridges (31) perpendicular to the translation of said conveyor belt (5), a slide (4) is placed between said screw conveyor (2) and said conveyor belt (5), said slide being equipped with guides, said guides having the shape of an inverse V, said first (7) and second (11) transport devices are both screw conveyors, said installation further comprising two material elevators (8 and 12) for transporting the material after said first and second screw conveyors (7 and 11), said second material elevator (12) transporting the material back to said buffer hopper (1) in case of an irradiation failure.
 13. The installation according to claim 9, wherein: said supply means consist of a first hopper (21), above a weighing station (22), comprising a second hopper (23) and placed in turn above a buffer hopper (1), leading to a screw conveyor (2), which takes the material through the wall of the irradiation cell (3), said screw conveyor (2) transports said material underneath said beam (6) for irradiation, said first (7) and second (11) transport devices are both screw conveyors, said installation further comprising two material elevators (8 and 12) for transporting the material after said first and second screw conveyors (7 and 11), said second material elevator (12) transporting the material back to said buffer hopper (1) in case of an irradiation failure. 